Four Sendai DI-RNAs have been isolated and characterized by electron microscopy and RNA-RNA annealing to be unique segments of the viral genome. Three of these DI-RNAs form circles at 100% frequency and these circles are held together by a double-stranded stems of approximately 150 base pairs. The ds-stems from three DI RNAs are identical by RNA-RNA hybridization suggesting that they derive from common sites on the non-defective (ND) genome, most probably the ends of the ND-genome. We intend to carry out experiments to determine if this is indeed the case. The DI RNAs will also be used to help separate the mRNAs and we hope to construct heteroduplexes between DI RNAs and ND-genome RNA. The examination of these heteroduplexes in the EM should tell us which viral sequences have been retained and which sequences have been deleted.